(1) Field of the Invention
The present invention relates to a method for stopping driving an image carrier and an image forming apparatus that performs the method, and in particular to technology for controlling process of stopping driving the image carrier after transfer of a toner image.
(2) Description of Related Art
In general, an electrophotographic image forming apparatus such as a copying machine and a printer performs image formation in the following manner. A developer supplies toner to an electrostatic latent image formed on an image carrier such as a photosensitive drum to develop the electrostatic latent image. The developed toner image is directly transferred onto a sheet, or is transferred onto another image carrier such as an intermediate transfer belt and then transferred onto a sheet. After that, the transferred toner image is thermally fixed to the sheet to form an image.
When the toner image is transferred onto the sheet, not all toner on the image carrier is transferred onto the sheet, but a certain amount of toner remains on a surface of the image carrier without being transferred.
The remaining toner can stain the sheet in the subsequent image formation. In addition, once the remaining toner is melted by heat of a fixing unit and adheres to the intermediate transfer belt, an image is not formed in an area of the intermediate transfer belt to which the toner adheres. This can lead to a white spot phenomenon. Therefore, it is required to remove the remaining toner prior to the subsequent image formation. Various methods for removing the remaining toner are known. Among them, commonly used is a method of scraping and collecting the remaining toner from the surface of the image carrier by sliding an elastic plate-like cleaning blade on the surface, because the method is simple and inexpensive.
This method, however, has a problem that the intermediate transfer belt is worn away by friction with the cleaning blade and, as a result, deterioration of the intermediate transfer belt is accelerated.
In view of the above problem, as a method for reducing a distance that the intermediate transfer belt travels until it stops to reduce the wear, a method of stopping rotating the intermediate transfer belt immediately after remaining toner passes a transfer position without cleaning has been proposed. According to this method, when the intermediate transfer belt is driven to rotate to perform the subsequent image formation, remaining toner is removed eventually.
However, a fixing unit is normally provided immediately downstream from the transfer position in a conveyance direction of a sheet, and thus, in the vicinity of the transfer position, the temperature tends to be increased by heat of the fixing unit. In the above method, the toner remaining on the intermediate transfer belt without being removed might be melted by the heat and adhere to the intermediate transfer belt.
Furthermore, in recent years, in order to promote energy savings by reducing a fixing temperature, toner that can melt and be fixed at a lower temperature has been developed. With the use of such toner, remaining toner melts at a lower temperature and adheres to the intermediate transfer belt easily.
As technology for preventing remaining toner on the intermediate transfer belt from melting, Japanese Patent Application Publication No. 2005-31503 discloses a structure in which an intermediate transfer belt (intermediate transfer member) is cooled by a cooling fan.
Furthermore, Japanese Patent Application Publication No. 2001-296755 discloses another structure in which an exhaust fan is provided to cool the intermediate transfer belt by letting the air out of the image forming apparatus, a cooling fan is provided to directly cool the intermediate transfer belt, and a heat pipe is provided inside a driven roller to cool the intermediate transfer belt via the driven roller.
However, the structures disclosed in Japanese Patent Application Publication No. 2005-31503 and Japanese Patent Application Publication No. 2001-296755 do not reduce a distance that the intermediate transfer belt travels until it stops after secondary transfer, and therefore do not reduce the wear of the intermediate transfer belt caused by the cleaning blade.
In addition, a cooling fan is not preferred in terms of energy savings, because power consumption is increased by driving the cooling fan.